Python Virtual Control Panel

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1. Introduction

Python Virtual Control Panel

The PyVCP (Python Virtual Control Panel) is designed to give the
integrator the ability to customize the AXIS interface with buttons and
indicators to do special tasks.

Hardware machine control panels can use up a lot of I/O pins and can
be expensive. That is where Virtual Control Panels have the advantage
as well as it cost nothing to build a PyVCP.

Virtual Control Panels can be used for testing or monitoring things to
temporarily replace real I/O devices while debugging ladder logic, or
to simulate a physical panel before you build it and wire it to an I/O
board.

The following graphic displays many of the PyVCP widgets.

2. Panel Construction

The layout of a PyVCP panel is specified with an XML file that
contains widget tags between <pyvcp> and </pyvcp>. For example:

<pyvcp><labeltext="This is a LED indicator"/><led/></pyvcp>

If you place this text in a file called tiny.xml, and run

halrun -I loadusr pyvcp -c mypanel tiny.xml

PyVCP will create the panel for you, which includes two widgets, a
Label with the text This is a LED indicator, and a LED, used for
displaying the state of a HAL BIT signal. It will also create a HAL
component named mypanel (all widgets in this panel are connected to
pins that start with mypanel.). Since no <halpin> tag was present
inside the <led> tag, PyVCP will automatically name the HAL pin for the
LED widget mypanel.led.0

For a list of widgets and their tags and options, see the widget
reference below.

Once you have created your panel, connecting HAL signals to and from
the PyVCP pins is done with the halcmd:

If you are new to HAL, the HAL basics chapter in the Integrator
Manual is a good place to start.

3. Security

Parts of PyVCP files are evaluated as Python code, and can take any
action available to Python programs. Only use PyVCP .xml files from a
source that you trust.

4. AXIS

Since AXIS uses the same GUI toolkit (Tkinter) as PyVCP, it is
possible to include a PyVCP panel on the right side of the normal AXIS
user interface. A typical example is explained below.

Place your PyVCP XML file describing the panel in the same directory
where your .ini file is. Say we we want to display the current spindle
speed using a Bar widget. Place the following in a file called
spindle.xml:

Here we’ve made a panel with a Label and a Bar widget, specified that
the HAL pin connected to the Bar should be named spindle-speed, and
set the maximum value of the bar to 5000 (see widget reference below
for all options). To make AXIS aware of this file, and call it at start
up, we need to specify the following in the [DISPLAY] section of the
.ini file:

PYVCP = spindle.xml

To make our widget actually display the spindle-speed it needs to be
hooked up to the appropriate HAL signal. A .hal file that will be run
once AXIS and PyVCP have started can be specified in the [HAL] section
of the .ini file:

POSTGUI_HALFILE = spindle_to_pyvcp.hal

This change will run the HAL commands specified in
spindle_to_pyvcp.hal. In our example the contents could look like
this:

net spindle-rpm-filtered => pyvcp.spindle-speed

assuming that a signal called spindle-rpm-filtered already exists.
Note that when running together with AXIS, all PyVCP widget HAL pins
have names that start with pyvcp..

This is what the newly created PyVCP panel should look like in AXIS.
The sim/lathe configuration is already configured this way.

5. Stand Alone

This section describes how PyVCP panels can be displayed on their own
with or without LinuxCNC’s machine controller.

To load a stand alone PyVCP panel with LinuxCNC use these commands:

loadusr -Wn mypanel pyvcp -g WxH+X+Y -c mypanel <path/>panel_file.xml

You would use this if you wanted a floating panel or a panel with a
GUI other than AXIS.

-Wn panelname -
makes HAL wait for the component panelname to finish loading
(become ready in HAL speak) before processing more HAL commands. This
is important because PyVCP panels export HAL pins, and other HAL
components will need them present to connect to them. Note the capital
W and lowercase n. If you use the -Wn option you must use the -c option
to name the panel.

pyvcp < -g> < -c> panel.xml -
builds the panel with the optional geometry and/or panelname from the
xml panel file. The panel.xml can be any name that ends in .xml. The
.xml file is the file that describes how to build the panel. You must
add the path name if the panel is not in the directory that the HAL
script is in.

-g <WxH><+X+Y> -
specifies the geometry to be used when constructing the panel. The
syntax is Width x Height + X Anchor + Y Anchor. You can set the size
or position or both. The anchor point is the upper left corner of the
panel. An example is -g 250x500+800+0 This sets the panel at 250 pixels
wide, 500 pixels tall, and anchors it at X800 Y0.

-c panelname -
tells PyVCP what to call the component and also the title of the
window. The panelname can be any name without spaces.

To load a stand alone PyVCP panel without LinuxCNC use this command:

loadusr -Wn mypanel pyvcp -g 250x500+800+0 -c mypanel mypanel.xml

The minimum command to load a pyvcp panel is:

loadusr pyvcp mypanel.xml

You would use this if you want a panel without LinuxCNC’s machine
controller such as for testing or a standalone DRO.

The loadusr command is used when you also load a component that will
stop HAL from closing until it’s done. If you loaded a panel and then
loaded Classic Ladder using loadusr -w classicladder,
CL would hold HAL open (and the panel) until you closed CL.
The -Wn above means wait for the component -Wn "name" to become ready.
(name can be any name. Note the capital W and lowercase n.)
The -c tells PyVCP to build a panel with the
name panelname using the info in panel_file_name.xml.
The name panel_file_name.xml can be any name but must end in .xml - it is the
file that describes how to build the panel. You must add the path name
if the panel is not in the directory that the HAL script is in.

An optional command to use if you want the panel to stop HAL from
continuing commands / shutting down. After loading any other components
you want the last HAL command to be:

waituser panelname

This tells HAL to wait for component panelname to close before
continuing HAL commands. This is usually set as the last command so that
HAL shuts down when the panel is closed.

6. Widgets

HAL signals come in two variants, bits and numbers. Bits are off/on
signals. Numbers can be float, s32 or u32. For more information on HAL
data types see the HAL Data section. The PyVCP widget
can either display the value of the signal with an indicator widget, or
modify the signal value with a control widget. Thus there are four
classes of PyVCP widgets that you can connect to a HAL signal. A fifth
class of helper widgets allow you to organize and label your panel.

Widgets for indicating bit signals: led, rectled

Widgets for controlling bit signals: button, checkbutton, radiobutton

Widgets for indicating number signals: number, s32, u32, bar, meter

Widgets for controlling number signals: spinbox, scale, jogwheel

Helper widgets: hbox, vbox, table, label, labelframe

6.1. Syntax

Each widget is described briefly, followed by the markup used, and a
screen shot. All tags inside the main widget tag are optional.

6.2. General Notes

At the present time, both a tag-based and an attribute-based syntax
are supported. For instance, the following XML fragments are treated
identically:

<ledhalpin="my-led"/>

and

<led><halpin>"my-led"</halpin></led>

When the attribute-based syntax is used, the following rules are used
to turn the attributes value into a Python value:

If the first character of the attribute is one of the following, it is
evaluated as a Python expression: {(["'

If the string is accepted by int(), the value is treated as an integer

If the string is accepted by float(), the value is treated as
floating-point

Otherwise, the string is accepted as a string.

When the tag-based syntax is used, the text within the tag is always
evaluated as a Python expression.

The examples below show a mix of formats.

Comments

To add a comment use the xml syntax for a comment.

<!-- My Comment -->

Editing the XML file

Edit the XML file with a text editor. In most cases you can right
click on the file and select open with text editor or similar.

HAL pins provide a means to connect the widget to something. Once
you create a HAL pin for your widget you can connect it to another
HAL pin with a net command in a .hal file. For more information on
the net command see the HAL Commands section.

6.3. Label

A label is a way to add text to your panel.

<label></label> - creates a label

<text>"text"</text> - the text to put in your label, a blank label can be
used as a spacer to align other objects.

<font>("Helvetica",20)</font> - specificy the font and size of the text

The above code produced this example.
Also showing a vertical box with relief.

6.6. Buttons

A button is used to control a BIT pin. The pin will be set True when
the button is pressed and held down, and will be set False when the
button is released. Buttons can use the following optional options.

<padx>n</padx> - where n is the amount of extra horizontal extra space.

<pady>n</pady> - where n is the amount of extra vertical extra space.

<activebackground>"color"</activebackground> - the cursor over color.

<fg> "color"</fg> - the forground color.

<bg>"color"</bg> - the background color.

<disable_pin>True</disable_pin> - disable pin.

Text Button

A text button controls a bit halpin. The halpin is false until the
button is pressed then it is true. The button is a momentary button.

The text button has an optional disable pin that is created when you
add <disable_pin>True</disable_pin>.

A checkbutton controls a bit halpin. The halpin will be set True when the
button is checked, and false when the button is unchecked. The checkbutton is a
toggle type button. The Checkbuttons may be set initially as TRUE or FALSE the
initval field A pin called changepin is also created automatically, which can
toggle the Checkbutton via HAL, if the value linked is changed, to update the
display remotely.

The above code produced this example.
The coolant checkbutton is checked.
Notice the extra spaces in the Chips text
to keep the checkbuttons aligned.

Radiobutton

A radiobutton will set one of the halpins true. The other pins are set false.
The initval field may be set to choose the default selection when the panel
displays. Only one radio button may be set to TRUE (1) or only the highest
number pin set TRUE will have that value.

<font> - is a Tkinter font type and size specification. One font that
will show up to at least size 200 is courier 10 pitch, so for a
really big Number widget you could specify:

<font>("courier 10 pitch",100)</font>

<format> - is a C-style format specified that determines how
the number is displayed.

s32 Number

The s32 number widget displays the value of a s32 number. The syntax
is the same as number except the name which is <s32>. Make sure the
width is wide enough to cover the largest number you expect to use.

The u32 number widget displays the value of a u32 number. The syntax
is the same as number except the name which is <u32>.

Bar

A bar widget displays the value of a FLOAT signal both graphically
using a bar display and numerically.
The color of the bar can be set as one color throughout its range (default
using fillcolor) or set to change color dependent upon the value of the halpin
(range1, range2 range3 must all be set, if you only want 2 ranges, set 2 of
them to the same color).

6.8. Number Inputs

Spinbox

Spinbox controls a FLOAT pin. You increase or decrease the value of the pin by
either pressing on the arrows, or pointing at the spinbox and rolling your
mouse-wheel. If the param_pin field is set TRUE(1), a pin will be created that
can be used to set the spinbox to an initial value and to remotely alter its
value without HID input.

Scale controls a float or a s32 pin. You increase or decrease the
value of the pin be either dragging the slider, or pointing at the
scale and rolling your mouse-wheel. The halpin will have both -f
and -i added to it to form the float and s32 pins. Width is the width
of the slider in vertical and the height of the slider in horizontal
orientation. If the param_pin field is set TRUE(1), a pin will be created that
can be used to set the spinbox to an initial value and to remotely alter its
value without HID input.

The Dial outputs a HAL float and reacts to both mouse wheel and
dragging. Double left click to increase the resolution and double right
click to reduce the resolution by one digit. The output is capped by
the min and max values. The <cpr> is how many tick marks are on the
outside of the ring (beware of high numbers). If the param_pin field is set
TRUE(1), a pin will be created that can be used to set the spinbox to
an initial value and to remotely alter its value without HID input.

6.9. Images

Image displays use only .gif image format. All of the images must be
the same size. The images must be in the same directory as your ini
file (or in the current directory if running from the command line with
halrun/halcmd).

Image Bit

The image_bit toggles between two images by setting the halpin to
true or false.

This example was produced from the above code.
Using the two image files fwd.gif and rev.gif.
FWD is displayed when selectimage is false
and REV is displayed when selectimage is true.

Image u32

The image_u32 is the same as image_bit except you have essentially
an unlimited number of images and you select the image by setting the
halpin to a integer value with 0 for the first image in the images list
and 1 for the second image etc.

Inside an Hbox, you can use the <boxfill fill=""/>, <boxanchor anchor=""/>
, and <boxexpand expand=""/> tags to choose how items in the box behave when
the window is re-sized. For details of how fill, anchor, and expand behave,
refer to the Tk pack manual page, pack(3tk). By default, fill="y",
anchor="center", expand="yes".

Vbox

Use a Vbox when you want to stack widgets vertically on top of each
other.

Inside a Hbox, you can use the <boxfill fill=""/>, <boxanchor anchor=""/>
, and <boxexpand expand=""/> tags to choose how items in the box behave
when the window is re-sized. For details of how fill, anchor, and expand
behave, refer to the Tk pack manual page, pack(3tk). By default, fill="x",
anchor="center", expand="yes".

Labelframe

A labelframe is a frame with a groove and a label at the upper-left
corner.

A table is a container that allows layout in a grid of rows and
columns. Each row is started by a <tablerow/> tag. A contained
widget may span rows or columns through the use of
the <tablespan rows= cols=/> tag. The sides of the cells to which
the contained widgets “stick”
may be set through the use of the <tablesticky sticky=/> tag. A
table expands on its flexible rows and columns.